In the ever increasing demands on mobility of society of today, it is popular to provide small and portable devices having imaging capability. The optical systems of the above type are thus implemented in handheld imaging devices, such as handheld scanners and electronic pens. In order to restrict the overall size of such a handheld device, it is desirable to make the optical system compact.
The optical system typically comprises an irradiating system including a radiation source for providing the irradiation of the object, and an imaging system including a two-dimensional radiation sensor for recording an image of the object. For handheld devices, the spatial orientation between the optical system and the object, which typically is a plane surface, such as a paper, may vary substantially. For example, during the process of writing with an electronic pen, the pen will frequently be held at varying angles to the paper. Thus, the spatial orientation of the paper also varies in relation to the radiation sensor and the radiation source. As the angle varies, the relation between the radiation sensor and the writing surface will be changed. This sets demands on an imaging system to adequately image the viewed part of the object for different angles between the pen and the paper.
Further, demands are set on the radiation source to irradiate the object properly. These demands are accentuated when the radiation source and the radiation sensor are arranged at positions that relate to the object in different ways, such as being arranged at different distances to the object and forming different angles to the object. In these cases, the radiation source needs to emit radiation in a sufficiently large solid angle in order to ensure that the viewed object area is irradiated irrespective of orientation changes between the handheld device and the object.
WO 03/001358 discloses an electronic pen, in which a camera unit, a light source and a writing implement are carried by a common mounting part which is arranged at the front end of the pen. This design aims at controlling the mutual location of relevant components in the pen. However, the assembly of this electronic pen is not entirely satisfactory. Further, the electronic pen still involves relatively long tolerance chains between the components of the camera unit and the light source, as well as an electrical coupling between the camera unit and a printed circuit board that may increase the manufacturing cost, decrease the durability of the pen, and introduce manual assembly steps in the production.
WO 03/025658 discloses an optical component which is designed to enable an irradiating system and an imaging system to share optical axis. Thus, irrespective of its orientation in relation to the object, the radiation source will irradiate the area of the object being imaged by the radiation sensor.
U.S. Pat. No. 5,939,702 discloses an optical reader, in which an emitter and a photodiode are mounted on a circuit board and a light pipe is used for communicating light between an external device, such as a paper having optical data, and the emitter and the photodiode. This optical reader forms merely a pointing means and provides no possibility of optical detection while using a writing functionality. Further, the optical reader is only capable of point detection and requires the reader to be moved for obtaining one- or two-dimensional data. Moreover, the emitter and the photodiode uses the same light pipe, which may cause the photodiode to detect light that comes directly from the emitter and has not interacted with the external device.